Over the past decade, there has been a concerted effort to reduce atmospheric pollution caused by volatile solvents which are emitted during the painting process. However, it is often difficult to achieve high quality, smooth coating finishes, such as are required in the automotive industry, without using organic solvents which contribute greatly to flow and leveling of a coating.
One of the major goals of the coatings industry is to minimize the use of organic solvents by formulating waterborne coating compositions which provide a smooth, high gloss appearance, as well as good physical properties including resistance to acid rain. Unfortunately, many waterborne coating compositions, particularly those containing metallic flake pigments, do not provide acceptable appearance because they deposit as a rough film under conditions of low humidity. Although smooth films can be obtained if the humidity is controlled within narrow limits, this often is not possible in industrial applications without incurring considerable expense.
Therefore, it would be desirable to provide a waterborne coating composition which is useful as an original finish for automobiles and which can be applied as a smooth film under a variety of humidity conditions.